The familiar side-mounted dynamo is the most widespread type for bicycles and, in terms of its mechanical and electrical structure, has been developed especially for operating incandescent bulbs. As their luminous efficiency falls dramatically when the voltage decreases and their filaments quickly burn out in the presence of excess voltage, in the middle of the last century performance characteristics were specified in the German Road Traffic Licensing Regulation (StVZO), which facilitate the direct connection of incandescent bulbs, but adherence to this specification comes at a high price:                the dynamo has an extremely high mechanical transmission ratio (i.e. high revs in relation to the traveling speed) so that it can generate sufficient output even at low speeds. At high speeds it is very loud.        intentionally high eddy current losses have been designed into the magnetic circuit in order to throttle the output voltage with increasing speed. The very low efficiency of the system not only requires a large design volume and weight but also a very high mechanical propulsive power with a correspondingly high braking effect.        Even high compressive force on the tire and the ribbing in the flank of the tire are barely sufficient to transfer the high peripheral force. Low levels of soiling or wet conditions are sufficient to cause the dynamo to slip.        
In order to guarantee reliable function in poor weather conditions, a change took place a number of years ago toward equipping bicycles for everyday use with hub dynamos as a standard feature. Admittedly, it is possible with modern magnetic materials of high flux density to keep the design volume and weight within tolerable limits, but, with a weight-to-power ratio of 400 g/W=133 kg/kW, the hub dynamo, is far below all technological standards. This is not so much due to the engineering design itself, but more to the principle that the output of all electrical machines rises or falls with rotational speed. The supposed advantages of the hub dynamo are at the same time its disadvantages: It is built into the spokes of the front wheel and can therefore only be retrofitted with great effort and often not all. It rotates only at the frequency of the wheel and hence far too slowly for an electrical machine. Consequently, it is heavy, too expensive and, above all, rotates permanently, generating additional friction, even when not required.
In the sport of cycling, the above-mentioned reasons mean that the hub dynamo has barely become established. Instead, the dominant system—if any—in this field has been removable, battery-powered lighting. Apart from their still relatively high weight, the batteries are a burden on the environment.
A solution similar to the approach in this invention is described in DE 195 45 680 [U.S. Pat. No. 5,932,943]: as is usual in the field of electrical engineering, this involves a three-phase current machine with coated thin dynamo sheets to minimize eddy current losses. To allow the entire system to operate, there is a clear functional separation between electricity generation (with optimum efficiency) and low-loss electronic power control. As this dynamo is driven by a friction wheel on the tire and has strong permanent magnets on the rotor, minimization of the magnetic torque was necessary, i.e. a differing number of magnets and slots. The dynamo is designed as an internal rotor and if reasons of production technology mean that the magnets are merely cemented in place, it only has limited stability to rotational speed: it is able to self-destruct if the centrifugal forces tear the magnets out of their mountings. Another disadvantage is the unfavorable ratio of the radii between the air gap and the outer contour of the housing.
In order to facilitate a sufficiently high rotational speed or high transmission ratio, the diameter of the friction wheel should exceed that of the air gap by as small a margin as possible. Due to the eccentric mounting of the friction wheel axle, this aspect is in fact taken into account but at the cost of a design that is not only extremely complex but could also be very prone to failure in the long term due to the dry and fast-rotating gearing. As the circuit board with rectifier and electronic power/voltage control is located directly in the dynamo housing and is tailored to this dynamo, only the version with three-phase current makes sense here because it is the only way to achieve the highest possible efficiency.
In the future, the bicycle is set to assume a growing role in the ecological transformation of our traffic systems. It is therefore important to exploit all opportunities to make cycling more attractive, i.e. safer, faster, more comfortable and, if possible, even cheaper. Hitherto unexploited opportunities exist in the field of bicycle lighting and particularly in relation to the dynamo.